Accessing the petroclival region through the extended endoscopic endonasal approach (EEA) is often difficult due to the paraclival carotid artery, which requires its skeletonization and lateral mobilization, as well as the use of angled scopes and instruments. Although the sublabial contralateral transmaxillary (CTM) corridor, combined with the EEA, was introduced to address these challenges, it has some limitations. The CTM port's endoscope or instrument is in the same horizontal plane as the instruments passing through the nostrils, causing “swording” with the endoscope. Additionally, the CTM requires medial pterygoid drilling contralateral to the petrous apex lesion risking the Vidian nerve and extensive maxillary sinus/osteo-meatal complex disruption increasing the nasal morbidity. To tackle these issues, we introduce a novel minimally invasive corridor to the petrous apex as a multiport strategy with EEA- the endoscopic precaruncular contralateral medial transorbital approach (cMTO). This cadaveric study aims to provide a morphometric comparison of the CTM and cMTO corridors for accessing the petrous apex via EEA in a controlled laboratory setting.
We dissected ten fresh, pre-injected human cadaveric specimens (20 sides) using neuronavigation to complete endoscopic cMTO and CTM on each side. We meticulously measured and compared several key parameters, including the working distance between the entry point and the target (petrous apex), the visualization angle, the angle of attack, and the surgical freedom afforded by each approach. We measured the visualization angle to assess the degree of “swording” between instruments and the endoscope tip in both the CTM and cMTO corridors.
The mean working distance between the entry points (orbital or maxillary) and the petrous apex was 67.1 ± 5.05 mm for the cMTO approach, significantly short compared to 75.62 ± 5.04 mm for the CTM approach (p-value <0.001). cMTO had a significantly better visualization angle (28.4 ± 3.27 degrees) than the CTM (24.42 ± 5.02 degrees, p-value <0.005). In the vertical plane, the mean angle of attack for the cMTO and CTM corridors was 9.80 and 8.47 degrees, respectively (p-value 0.186). In the horizontal plane, the angle of attack for the cMTO corridor was 8.53 degrees, compared to 10.12 degrees for the CTM corridor (p-value 0.103). The cMTO approach offered slightly more surgical freedom with 655.34 mm2 of space compared to the CTM approach's 639.41 mm2 (p-value 0.79).
Our results show that the cMTO corridor is a better option for targeting petroclival lesions using a multiport strategy in combination with the endoscopic endonasal approach (EEA) compared to the CTM corridor. The cMTO corridor offers a similar lateral working angle to the CTM while providing additional benefits such as a shorter distance between the entry point and the target (petrous apex), a wider visualization angle, and more effective maneuverability for surgical instruments. However, future clinical studies are needed to validate these anatomic study results in patients.
